In the past, gyroscopes and gyroscopic devices were constructed of relatively large and expensive electromagnetic devices. These electromagnetic devices incorporated coils and position sensors mounted for relatively high speed, continuous rotational movement.
Eventually, micromechanical rate gyros were developed which included components formed by semiconductor processing techniques. While these devices are relatively small and utilize vibrational motion rather than continuous rotary motion, they are relatively insensitive and costly to manufacture.
Generally, the micromechanical rate gyros are constructed with a central mass, which because of the size of the gyro is very small and requires some very heavy material such as gold to provide sufficient mass. The central mass is mounted in a gimbal structure including mutually orthogonal flexible axes, with the mass and gimbal structure generally lying in a common plane. The central mass and inner mounting gimbal are oscillated or vibrated about a first of the orthogonal axes and rotational movement about an axis perpendicular to the common plane produces vibrational movement about the other of the orthogonal axes, due to the Coriolis, or gyroscopic, effect.
The described micromechanical rate gyro has several problems. Specifically, the centrally mounted mass is expensive and difficult to manufacture. It is difficult to achieve a large enough mass to provide sufficient inertia for good sensitivity and this construction reduces sensing capacitor sensitivity by increasing the distance between capacitive plates. Also, if the mass is offset even slightly within the gimballed mounting a noticeable sensitivity to cross-axis acceleration is produced. Second, the amount of vibrational movement is limited by the fact that the planar constructed gimbal system is mounted adjacent to a planar surface and increasing the distance between the gimbal system and the planar surface substantially increases the size of the device, which reduces sensitivity due to increased capacitor spacing as well as increasing the cost and complexity of construction. Further, by constructing the device so that the input axis is perpendicular to the common plane, the device is limited to a single axis device. Since the device only senses movement about a single axis, three of the devices must be mounted with the input axes in a mutually orthogonal relationship to sense movement in all directions.
In attempts to reduce the size and cost of accelerometers, some of the prior art devices have been constructed using semiconductor manufacturing techniques. These devices generally consist of a plate, formed of metal or the like, which is mounted for pivotal movement on a substrate. The plate is positioned parallel to a planar surface of the substrate and forms one or more capacitances therewith. When the plate moves, due to an acceleration force thereon, the capacitances change. This change is sensed by connected electronic circuits and converted to a signal representative of the acceleration.
Gyroscopes and accelerometers are useful in inertial guidance packages to sense movement, or acceleration, of a vehicle in all directions. From this information the position of the vehicle can be determined at all times. Gyroscopes and accelerometers, such as those described above, are manufactured as a single axis device. To obtain an indication of movement in all directions, three of the prior art gyroscopes and/or accelerometers must be positioned so that the sensitive axes are mutually orthogonal. This means that the final package is still relatively large since one or more of the gyroscopes and/or accelerometers must be positioned at an angle to the others and the entire package can never be formed as a single planar package. Further, since each gyroscope and/or accelerometer is constructed on a separate semiconductor substrate, signals must be communicated between chips and, it is a well known fact, that large amounts of power are required to amplify, buffer and communicate signals between chips and noise is induced which reduces the sensitivity of the system.